As is well known, a magnetic disk drive comprises a magnetic disk as a recording medium. The magnetic disk is hereinafter sometimes simply referred to as a disk. Servo data (servo patterns) is recorded, for example, on both surfaces of the disk. The servo data is used to position a head at a target position on the disk.
Recent magnetic disk drives have a function (what is called a self-servo writing function) in which the magnetic disk drive itself writes servo data to both surfaces of the disk. The self-servo writing is generally carried out as follows. First, it is assumed that the disk comprises a first surface and a second surface and that original servo data is already recorded on the first surface. It is also assumed that a first head and a second head are arranged in association with the first surface and the second surface, respectively. In this case, the first head is positioned at a target position on the first surface (that is, tracking is performed) based on the original servo data recorded on the first surface. That is, the first surface is used as a tracking surface. In this state, the first head and the second head simultaneously write the servo data to the first surface and the second surface, respectively. The second surface, which is not used for tracking, is hereinafter referred to as the non-tracking surface or the servo writing surface. Additionally, the self-servo writing, in which the servo data is written simultaneously to each of the opposite surfaces of the disk, is hereinafter referred to as servo writing using a bank write method.
Furthermore, in recent years, magnetic disk drives have emerged which comprise microactuators (micromotion actuators) associated with the respective surfaces of the disk. Compared to a primary actuator (coarse motion actuator, VCM actuator), each of the microactuators enables the corresponding head to make micromotion independently of the other head. Thus, in the magnetic disk drive comprising microactuators, a first operation amount is provided to a microactuator (first microactuator) associated with the first surface (tracking surface) of the disk. On the other hand, a second operation amount that is different from the first operation amount is provided to a microactuator (second microactuator) associated with the second surface (non-tracking surface) of the disk.
As described above, in the magnetic disk drive comprising the first and second microactuators, the first and second microactuators are driven independently. Thus, the first and second microactuators are provided independently with the first and second operation amounts, respectively.
Here, it is assumed that data is written simultaneously to both surfaces of the disk as is the case with the servo writing using the bank write method. In such a case, if an operation amount obtained by inverting the polarity of the first operation amount is used as the second operation amount, positioning errors reverse in phase between the first surface and the second surface of the disk can be inhibited. However, positioning errors the same in phase on between the first surface and the second surface of the disk increase on the second surface. Thus, there has been a demand to also reduce positioning errors on the second surface of the disk if the first surface of the disk is used as a tracking surface.